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Journal of the Mexican Chemical Society

Print version ISSN 1870-249X


MONTES-ROJAS, Antonio  and  CHAINET, Eric. Electromicrogravimmetric Study of the Effect of Cl- Anions on Thallium Underpotential Deposition Onto Gold. J. Mex. Chem. Soc [online]. 2005, vol.49, n.4, pp.336-343. ISSN 1870-249X.

The effect of chloride adsorption on underpotential deposition of thallium onto gold electrode was studied using cyclic voltammetry coupled with microgravimetry. The results obtained suggest the existence of two potential regions with different processes occurring during Tl UPD in the presence of anions. In the first zone, at low coverage, there are two simultaneously occurring processes: desorption of all chloride atoms, which are adsorbed on the gold substrate prior to the onset of Tl UPD, and thallium adsorption on the energetically most favorable sites (grain boundaries, steps, etc) present on the electrode surface. During these processes a strong interaction among thallium atoms is induced by the presence of chloride atoms on the adjacent sites. This strong interaction generates sharper current peaks in the voltammogram, associated with the above processes, and their displacement towards cathodic potentials proportional to the anion concentration. However, in the second potential zone at high coverage, the adsorption of thallium atoms takes place on the least accessible sites (terraces) on the gold substrate. In this type of sites, the effect of the presence of chloride atoms on the UPD process is unimportant.

Keywords : electromicrogravimmetry; underpotential deposition; thallium; adsorption; chloride.

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